Pci Express Specifications (2025)

In this post, we are going to demystify PCI Express specifications. We’ll break down the jargon, compare the generations, and help you understand what you need to look for in your next build.

| Capability | Description | |------------|-------------| | | One physical device appears as multiple virtual functions (VFs) to VMs. | | Address Translation Services (ATS) | Device-managed IOMMU page tables. | | Process Address Space ID (PASID) | Fine-grained device access to process-specific memory. | | Page Request Interface (PRI) | Device can request OS to page in memory. | | Multi-Function Device | Up to 8 functions per device (e.g., GPU + audio + USB). | | Alternative Protocol (AltProto) | Allow non-PCIe protocols (e.g., CXL) over same PHY. | pci express specifications